Effect of power ultrasound on pH change in water saturated with air, oxygen, nitrogen, argon and mixtures

Sonication was carried out under atmosphere of air, oxygen, nitrogen, argon , or their gas mixtures. The value of pH in water for different dissolved g ases was obtained under a constant ultrasonic intensity. The ultrasonic int ensity in the reaction vessel was measured by use of the decomposition reac tion of porphyrin in water. Under an air atmosphere, the pH value changed f rom 7 to 4.3 for an irradiation time of 30 min and after that the pH value approached to 3.7. On the other hand, the pH values for water saturated wit h Ar, Nz or Oz slightly decreased. In the mixture of Ar, Nz and Oz, the min imum pH in water saturated with the Ar+O-2 mixture was observed around 60 % of Ar, and that saturated with the Ar+ (N-2 and O-2) mixture at around 30 % of Ar. The amount of OH radical produced on sonication was consistent wit h that estimated from products obtained by decomposition of water. From the se results, it is concluded that the decrease of pH is influenced not only by N-2, but also by O-2.